A conventional communication system allows for communication through a communications channel, such as a microwave radio link, a satellite channel, a fiber optic cable, a hybrid fiber optic cable system, or a copper cable to provide some examples. The conventional communication system includes a conventional communications transmitter to transmit one or more information signals to a conventional communications receiver via the communication channel.
The conventional communications transmitter often modulates the information signals using a quadrature modulating scheme. Quadrature modulating entails modulating the information signals with two transmitter carrier waves that are substantially similar in frequency but exhibit a 90-degree phase offset from one another. The information signals are modulated with a first transmitter carrier wave in an in-phase transmitter processing branch to provide an in-phase (I) signal and a second transmitter carrier wave in a quadrature phase transmitter processing branch to provide a quadrature phase (Q) signal. The I signal and Q signal are then combined to provide a transmitted communications signal.
The conventional communications receiver receives a received communications signal as it passes through the communications channel to provide one or more recovered information signals. The conventional communications receiver often demodulates the received communications signal using a quadrature demodulating scheme. The received communications signal is separated into a recovered I signal and a recovered Q signal. The conventional communications receiver operates on the recovered I signal in a conventional in-phase receiver processing branch using a first receiver carrier wave and the recovered Q signal in a conventional quadrature phase receiver processing branch using a second receiver carrier wave. The first receiver carrier wave and the second receiver carrier wave are substantially similar in frequency but are offset in phase by approximately 90-degrees from one another. The conventional communications receiver then combines the recovered I signal and the recovered Q signal to provide a recovered sequence of data.
Ideally, a gain response and/or a phase response of the conventional transmitter processing branches and/or the conventional receiver processing branches are identical. In practice, however, the gain response and/or phase response of these processing branches may not be exactly equal causing an in-phase/quadrature phase (I/Q) imbalance. This I/Q imbalance may cause a gain offset and/or phase offset between the recovered I signal and the recovered Q signal which along with other I/Q imbalances of the conventional communications system may degrade an ability of the conventional communications receiver to recover the recovered sequence of data from the received communications signal.
Commonly, the conventional communications receiver may be calibrated at a manufacturing factory to compensate for these I/Q imbalances. Calibration of the conventional communication receiver at the manufacturing factory often involves an estimation of the I/Q imbalance in the communication system under controlled operating conditions. The conventional communication receiver, however, may operate in conditions that differ from the controlled operating conditions at the manufacturing factory. For example, the conventional communication receiver may operate at temperatures that differ from the temperature under the controlled operating conditions and/or at operational frequencies that differ from the operational frequencies under the controlled operating conditions. As a result, the calibration of the conventional communications receiver at the factory may not adequately compensate for the I/Q imbalance in conditions that differ from the controlled operating conditions at the manufacturing factory.
The I/Q imbalance is compensated for in the conventional communication receiver by programming specific calibration parameters resulting from the controlled operating conditions into each conventional communication receiver. Process variations in semiconductor fabrication may cause the specific calibration parameters to differ from one conventional communication receiver to another. As a result, each conventional communication receiver may require specific calibration parameters that are unique for that particular conventional communication receiver which, in turn, requires the manufacturing factory to calibrate each conventional communication receiver.
Thus, there is a need for an apparatus and/or a method to compensate for I/Q imbalances in a communication receiver that overcomes the shortcomings described above. Further aspects and advantages of the present invention will become apparent from the detailed description that follows.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.